Medical navigation systems are known and used to provide operating physicians with visual assistance during operations. Such visual assistance may include indicating a location of positionally determined and tracked instruments with respect to particular parts of the patient's body. The information concerning the body parts can be previously or intra-operatively ascertained using imaging methods. Further, with the aid of an initial registration procedure, the spatial positions of the patient, the corresponding image data and the instruments used in the operating theater can be assigned such that navigation and/or image-assisted surgery can be subsequently performed. An exemplary navigation system is described in DE 19 639 615 C2.
A fundamental concept of such image-guided surgery systems that use a spatial arrangement of marker elements may be based on the arrangement of marker elements (e.g., a reference array that includes one or more marker elements) on instruments, patients or treatment-assisting apparatus. The spatial arrangement of marker elements, which are formed as rigid bodies, may be used in a defined coordinate system or may define the coordinate system. More specifically, these rigid marker bodies can be translated into a reference system, compared with a reference system that is predetermined by a reference set-up, or compared with an absolute position as defined by a tracking system.
Alternatively, geometries of the spatial arrangement of marker elements may be predefined and stored in the navigation system. This can apply to navigation systems in accordance with the above-referenced document or also to other navigation and/or tracking systems (optical tracking systems, magnetic tracking systems, ultrasound tracking systems, etc.). In other words, a number of different and characteristic spatial arrangements of marker elements may be previously known to and/or stored in the navigation system, wherein the characteristic spatial arrangements of marker elements each correspond to a particular reference array (group of marker elements) or are already assigned to an instrument.
Further, the geometry of the instrument also may be stored in the navigation system. If the navigation system, via data obtained from the tracking system, identifies one or more particular and characteristic spatial arrangements of marker elements, the one or more spatial arrangements of marker elements can be compared with the previously stored spatial arrangements of marker elements. If these previously stored spatial arrangements of marker elements are each associated with a particular instrument or reference array, then the instrument and/or reference array also can be identified. In such systems, it is preferable that the rigid geometries defined by the spatial arrangement of marker elements have a high degree of accuracy. This enables the spatial arrangement of marker elements to be properly identified, as well as enabling the calculation of six degrees of freedom (three-dimensional position +orientation on the three spatial axes) for localizing the instrument.